1. Field of the Invention
This invention relates to a multiple disc clutch apparatus used for a driving system, such as a transmission and a center differential locking device for vehicles.
2. Description of the Prior Art
In general, in a multiple disc clutch, a plurality of input side clutch plates fixed to an input side rotary body so that these clutch plates cannot be turned relatively to the input side rotary body but can be moved slidingly in the axial direction at either the outer circumferential edges thereof or the inner circumferential edges thereof, and a plurality of output side clutch plates fixed to an output side rotary body so that these clutch plates cannot be turned relatively to the output side rotary body but can be moved slidingly in the axial direction at the circumferential edges thereof which are on the opposite side of those of the input side clutch plates at which the input side clutch plates are fixed to the input side rotary body are laminated alternately in the axial direction, the resultant laminated body of the input and output side clutch plates being pressed by a clutch piston, which is provided at one side of the laminated body with respect to the direction of the axis of rotation thereof, toward the other side thereof so that the laminated clutch plates are pressed against one another to generate a frictional force on the frictional surfaces thereof, whereby the input side rotary body and output side rotary body are put in a frictionally connected state, i.e. a power transmitted state.
The conventional transmissions for vehicles, such as automobiles include a transmission disclosed in, for example, Japanese Patent Laid-open No. 191631/1983, in which a valve body in the interior of the transmission is provided therein with various types of valves, such as a pressure regulator valve adapted to regulate hydraulic pressure from an oil pump, or a manual valve adapted to switch the hydraulic pressure, which is regulated by the pressure regulator valve, in accordance with the vehicle steering condition, and oil passages. The hydraulic pressure referred to above operates the clutch piston in the multiple disc clutch to enable the rotational force from the engine on the input side to be transmitted to a desired gear on the output side.
Japanese Patent Application No. 159836/1986 discloses an embodiment in which an electromagnetic multiple disc clutch unit shown in FIG. 3 is used, of a center differential locking device for four-wheel drive vehicles. In this electromagnetic multiple disc clutch unit 70, a solenoid means 71 and a multiple disc clutch 72 are unitarily formed. In this center differential locking device for four-wheel drive vehicles, the electromagnetic multiple disc clutch unit 70 is used as a center differential locking means, and the attractive force of the solenoid means 71 in the electromagnetic multiple disc clutch unit 70 can be varied very easily by merely controlling the amperage of the solenoid 73.
In general, the torque capacity of a multiple disc clutch is determined depending upon the diameter and number of the clutch plates, and the level of the attractive force of the solenoid. Therefore, if the outer diameter of the electromagnetic multiple disc clutch is limited, the diameter of the clutch plates as well as that of the solenoid in the solenoid means are limited. Consequently, the attractive force of the solenoid, which is determined by the cross-sectional area of an iron core, cannot be set to higher than a certain level.